<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div>点我</div>
    <script>
        function addEventListener(elem, type, func) {
            if (elem.addEventListener) {
                elem.addEventListener(type, func)
            } else if (elem.attachEvent) {
                elem.attachEvent(type, func)
            } else {
                elem['on' + type] = func
            }
        }
        const div = document.querySelector('div')
        addEventListener(div,'click', function(){
            alert('点击了')
        })
    </script>
</body>
</html>